Method and apparatus providing multi-planed array memory device

ABSTRACT

A three dimensional variable resistance memory array and method of forming the same. The memory array has memory cells in multiple planes in three dimensions. The planes of the memory cells include shared interconnect lines, dually connected to driving and sensing circuits, that are used for addressing the cells for programming and reading. The memory array is formed using only a single patterned mask per central array plane to form the memory cells of such planes.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices, and inparticular resistance-variable memory devices, such as phase-changememory, and methods of forming the same.

BACKGROUND OF THE INVENTION

Non-volatile (or less-volatile) memories are important elements ofintegrated circuits due to their ability to maintain data absent a powersupply. Phase change materials, among other resistance-variable memorytypes, have been investigated for use in non-volatile memory cells.Phase change memory cells include phase change materials, such aschalcogenide alloys, which are capable of stably transitioning betweenamorphous and crystalline phases. Each phase exhibits a particularresistance state and the resistance states distinguish the logic valuesof the memory cell. Specifically, an amorphous state exhibits arelatively high resistance, and a crystalline state exhibits arelatively low resistance. A phase change memory cell has a phase changematerial between first and second electrodes. As an example, the phasechange material is a chalcogenide alloy, such as described in U.S.Patent Application Publication No. 2007/0029537 (application Ser. No.11/194,623) and U.S. Patent Application Publication No. 2007/0034905(application Ser. No. 11/199,257), each of which are incorporated byreference herein. Phase change memory elements can comprise Ge, Se, Sb,and/or Te (e.g., Ge₂Sb₂Te₅), or other chalcogenide-comprising alloys,with other optional materials positioned between two electrodes forsupplying current to the element.

A portion of the phase change material is set to a particular resistancestate according to the amount of current applied via the electrodes. Toobtain an amorphous state, a relatively high write current pulse (areset pulse) is applied to the phase change cell to essentially melt aportion of the material for a first period of time. The current isremoved and the cell cools rapidly to a temperature below the glasstransition temperature, which results in the portion of the materialretaining an amorphous phase. To obtain a crystalline state, a lowercurrent write pulse (a set pulse) is applied to the phase change cellfor a second period of time (typically longer in duration than the firstperiod of time) to heat the material to a temperature below its meltingpoint. This causes the amorphous portion of the material to crystallizeor re-crystallize to a crystalline phase that is maintained once thecurrent is removed and the cell is rapidly cooled.

As in any memory type, it is a goal in the industry to have as dense amemory array as possible, so it is desirable to increase the number ofmemory cells in an array of a given chip area. In pursuing this, memoryarrays have been designed in multiple planes in three dimensions,stacking planes of memory cells above one another. However, it istypical in the art to require many masks per memory array level for theformation of features of the memory cells and connecting circuitry. Itis not uncommon for ten to twenty masks to be required per level duringfabrication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows a portion of a memory array during a stage offabrication; FIG. 1 b shows a cross section of the array shown in FIG. 1a through line A-A.

FIG. 2 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 1 a; FIG. 2 b shows a crosssection of the array shown in FIG. 2 a through line A-A.

FIG. 3 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 2 a; FIG. 3 b shows a crosssection of the array portion shown in FIG. 3 a through line A-A.

FIG. 4 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 3 a; FIG. 4 b shows a crosssection of the array portion shown in FIG. 4 a through line A-A.

FIG. 5 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 4 a; FIG. 5 b shows a crosssection of the array portion shown in FIG. 5 a through line A-A.

FIG. 6 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 5 a; FIG. 6 b shows a crosssection of the array portion shown in FIG. 6 a through line A-A.

FIG. 7 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 6 a; FIG. 7 b shows a crosssection of the array portion shown in FIG. 7 a through line A-A.

FIG. 8 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 7 a; FIG. 8 b shows a crosssection of the array portion shown in FIG. 8 a through line A-A; FIG. 8c shows a cross section of the array portion shown in FIG. 8 a throughlike B-B; FIG. 8 d shows a cross section of the array portion shown inFIG. 8 a through line C-C; and FIG. 8 e shows a cross section of thearray portion shown in FIG. 8 a through line D-D.

FIG. 9 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 8 a; FIG. 9 b shows a crosssection of the array portion shown in FIG. 9 a through line A-A; FIG. 9c shows a cross section of the array portion shown in FIG. 9 a throughlike B-B; FIG. 9 d shows a cross section of the array portion shown inFIG. 9 a through line C-C; and FIG. 9 e shows a cross section of thearray portion shown in FIG. 9 a through line D-D.

FIG. 10 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 9 a; FIG. 10 b shows across section of the array portion shown in FIG. 10 a thorough line A-A;FIG. 10 c shows a cross section of the array portion shown in FIG. 10 athrough like B-B; FIG. 10 d shows a cross section of the array portionshown in FIG. 10 a through line C-C; and FIG. 10 e shows a cross sectionof the array portion shown in FIG. 10 a through line D-D.

FIG. 11 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 10 a; FIG. 11 b shows across section of the array portion shown in FIG. 11 a through line A-A;FIG. 11 c shows a cross section of the array portion shown in FIG. 11 athrough like B-B; FIG. 11 d shows a cross section of the array portionshown in FIG. 11 a through line C-C; and FIG. 11 e shows a cross sectionof the array portion shown in FIG. 11 a through line D-D.

FIG. 12 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 11 a; FIG. 12 b shows across section of the array portion shown in FIG. 12 a through line A-A;FIG. 12 c shows a cross section of the array portion shown in FIG. 12 athrough like B-B; FIG. 12 d shows a cross section of the array portionshown in FIG. 12 a through line C-C; and FIG. 12 e shows a cross sectionof the array portion shown in FIG. 12 a through line D-D.

FIG. 13 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 12 a; FIG. 13 b shows across section of the array portion shown in FIG. 13 a through line A-A;FIG. 13 c shows a cross section of the array portion shown in FIG. 13 athrough like B-B; FIG. 13 d shows a cross section of the array portionshown in FIG. 13 a through line C-C; and FIG. 13 e shows a cross sectionof the array portion shown in FIG. 13 a through line D-D.

FIG. 14 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 13 a; FIG. 14 b shows across section of the array portion shown in FIG. 14 a through line A-A;FIG. 14 c shows a cross section of the array portion shown in FIG. 14 athrough like B-B; FIG. 14 d shows a cross section of the array portionshown in FIG. 14 a through line C-C; and FIG. 14 e shows a cross sectionof the array portion shown in FIG. 14 a through line D-D.

FIG. 15 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 14 a; FIG. 15 b shows across section of the array portion shown in FIG. 15 a through line A-A;FIG. 15 c shows a cross section of the array portion shown in FIG. 15 athrough like B-B; FIG. 15 d shows a cross section of the array portionshown in FIG. 15 a through line C-C; and FIG. 15 e shows a cross sectionof the array portion shown in FIG. 15 a through line D-D.

FIG. 16 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 15 a; FIG. 16 b shows across section of the array portion shown in FIG. 16 a through line A-A;FIG. 16 c shows a cross section of the array portion shown in FIG. 16 athrough like B-B; FIG. 16 d shows a cross section of the array portionshown in FIG. 16 a through line C-C; and FIG. 16 e shows a cross sectionof the array portion shown in FIG. 16 a through line D-D.

FIG. 17 a shows a portion of the memory array during a stage offabrication subsequent to that shown in FIG. 16 a; FIG. 17 b shows across section of the array portion shown in FIG. 17 a through line A-A;FIG. 17 c shows a cross section of the array portion shown in FIG. 17 athrough like B-B; FIG. 17 d shows a cross section of the array portionshown in FIG. 17 a through line C-C; and FIG. 17 e shows a cross sectionof the array portion shown in FIG. 17 a through line D-D.

FIG. 18 shows a processor system incorporating a memory circuitcomprising an array portion as shown in FIG. 17 a.

FIG. 19 shows a block diagram of circuit connections for a threedimensional memory array.

FIG. 20 shows a simplified circuit diagram for shared interconnect linesof a memory array.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to variousspecific embodiments of the invention. These embodiments are describedwith sufficient detail to enable those skilled in the art to practicethe invention. It is to be understood that other embodiments may beemployed and that various structural, logical and electrical changes maybe made without departing from the spirit or scope of the invention.

The term “substrate” used in the following description may include anysupporting structure including, but not limited to, a semiconductorsubstrate that has an exposed substrate surface. A semiconductorsubstrate should be understood to include silicon, silicon-on-insulator(SOI), silicon-on-sapphire (SOS), doped and undoped semiconductors,epitaxial layers of silicon supported by a base semiconductorfoundation, and other semiconductor structures. When reference is madeto a substrate or wafer in the following description, previous processsteps may have been utilized to form regions or junctions in or over abase semiconductor or foundation. The substrate need not besemiconductor-based, but may be any support structure suitable forsupporting an integrated circuit, including, but not limited to, metals,alloys, glasses, polymers, ceramics, and any other supportive materialsas is known in the art. Further, substrate can include circuitry, suchas logic or access circuitry, and insulating layers so as to provide aplatform upon which to form other integrated circuit devices.

Embodiments of the invention relate to resistance variable memorydevices and methods of forming a three dimensional, i.e., stackedplanes, array of such devices. Although the embodiments are described asbeing a phase change memory type, this is for illustrative purposessince the array architecture and methods of forming same apply broadlyto other resistance variable memory types, such as, for example,programmable conductor memory, polymer memory, and others that can beused in a cross point architecture.

The embodiments of the invention are now explained with reference to thefigures, which illustrate exemplary embodiments and throughout whichlike reference numbers indicate like features. A portion of a phasechange memory array in accordance with an embodiment of the invention isshown in FIG. 17 a and FIGS. 17 b, 17 c, 17 d, and 17 e, which showvarious cross sections of the array portion shown in FIG. 17 a. Crosssectional views shown in FIGS. 17 b and 17 d show the layout of planes101, 103, 105, 107 of memory cells and cross sectional views shown inFIGS. 17 c and 17 e show the isolation of the memory cells by insulatingmaterial.

As shown in these figures, the array 100 has a stacked configuration ofphase change memory cells 102, 104, 106, and 108 (see dashed ringsidentifying the cells), each arranged in a plane 101, 103, 105, 107 ofmany memory cells, each including an electrode line, e.g., 28, a phasechange material, e.g., 26, a silicide diode material, e.g., 24, a polydiode material, e.g., 14, and another electrode, e.g., 12, for memorycell 102, which is exemplary of the other cells in the multiple planes101, 103, 105, 107. At least the poly diode material, e.g., 14, andelectrode line, e.g., 28, are within sidewall spacers, e.g., 20, thatdefine the stack dimensions of the memory cell, e.g., 102. The diodes(e.g., materials 14 and 24) are access devices for the memory elements,e.g., phase change material 26. The access devices need not necessarilybe diodes, but can be other two-terminal devices, such as rectifiers orthreshold switching devices.

The memory cells 102, 104, 106, 108 are defined at the cross pointintersections of electrode lines, e.g., 12 and 28, 28 and 44, 44 and 58,58 and 72, and the stacked configuration of the memory cells 102, 104,106, 108 is shown by the layering of the phase change material 26, 42,56, 70. Electrode lines, e.g., 12, 28, 44, 58, 72, are arranged in across point architecture and interconnect memory cells positioned alongthe same lines. Four memory cell planes 101, 103, 105, 107 are shown inthis way, with each such plane 101, 103, 105, 107 having a twodimensional array of multiple memory cells, e.g., in the X, Y plane. TheX, Y, Z dimensions are shown in FIGS. 17 a, 17 b, and 17 d. The planes101, 103, 105, 107 of memory cells are sacked in the Z dimension so asto provide a three dimensional array where any single memory cell can beaddressed for programming or reading by its X, Y, Z coordinates.Although four such planes 101, 103, 105, 107 are shown in the figures,it should be understood that fewer or greater planes of memory cells canbe included in the array 100.

Each electrode line 28, 44, and 58 that is not the array's 100 top-most,e.g., 72, or bottom-most electrode line, e.g., 12, can serve as both abit line and as a wordline in addressing memory cells for programmingand reading. As shown in FIG. 17 b, for example, the electrode line 28is configured so that it serves as a bit line for memory cell 102 and asa wordline for memory cell 104 as each respective memory cell 102, 104is addressed for reading or writing. Although the terms bit line andwordline originated in relation to DRAM technology to indicate the linecarrying stored information signal and the line carrying an accesscontrol signal, respectively, herein they are used to indicate two crosspoint arranged, intersecting, interconnect lines for addressing a memorycell in a memory array and just as well could be called row lines andcolumn lines or simply, interconnect lines.

The structure of the array 100 allows the central array planes, i.e.,not necessarily the top-most or bottom-most, such as the planes 103 and105 incorporating memory cells 104 and 106, respectively, to befabricated with a single mask per plane and, potentially, a single maskpattern for all such planes, which makes processing faster, simpler, andless expensive when compared to techniques requiring multiple masks formemory array layer fabrication. Because the memory cells, e.g., 104, arecomposed of stacks of layers defined by the dimensions of a hard mask(FIGS. 2 b to 16 e) 16, 32, 48, 62, and sidewall spacers 36, 54, 68, thephotolithographic mask (e.g., FIG. 8 d, 34) that defines the hard mask,e.g., 32, dimension (when etched) is the only mask needed during thefabrication of the respective memory cell plane. The formation of thesidewall spacers during processing, which does not require another mask,completes the definition of the memory cell dimensions and, so, only asingle mask is needed.

This cross-point arrangement of the array 100 structure allows for aself-aligned process in forming the memory elements. A self-alignedmemory element enables higher density memory arrays in a productionenvironment than would be feasible with memory elements which must haveother layers aligned, such as contacts. Masking techniques such as pitchmultiplication, as described in U.S. patent application Ser. Nos.11/214,544 and 11/514,117, and U.S. Pat. No. 5,328,810, incorporatedherein by reference, may be utilized in accordance with the invention.

A self-aligned cross-point structure created with an orthogonalline/space pattern allows high density lines without the tightalignment/registration normally required for memory element fabrication.Typically, the maximum allowed registration error is ⅓ f (where f is theminimum feature line/space dimension), but with a self-alignedcross-point technology, the only alignment requirement is in connectingthe ends of the lines to drivers and sense devices. While this involvessome overhead of area at the edges of the array 100, it allows one toapproach a 4 f footprint per memory element at very small dimensions forf, e.g., about 18-50 nm. Stacking such memory elements in the waydescribed herein makes the memory array density even higher andapproaches a 1 f footprint/memory element for a 4-tier stack of suchmemory elements as shown in FIGS. 17 b-17 e. Thus, higher densityproduct is enabled by a stacked self-aligned cross point memory elementstructure as described and claimed herein.

FIG. 20 a shows how this array 100 configuration includes a driver 300and sense 302 circuit connected to each of the central electrode lines28, 44, and 58 such that the driver circuit 300 of a respectiveelectrode line, e.g., 28, is used with the memory cell 104 of one planeof memory cells, and the sense circuit of that respective line, e.g. 28,is used with the memory cell 102 of an adjacent plane, e.g., 101 (FIG.17 b) of memory cells. The memory cell 104 (also FIG. 17 b) can beconnected to driving and sensing circuitry by the interconnect electrodelines 28 and 44 and access devices 304, such as gated transistors. Whenone of the driver 300 and sense circuit 302 is active on a givenelectrode line, the other is disabled.

The electrode line 28 has a sense circuit 302 and a driver circuit 300that can be connected to the terminal ends of the line 28 by a via to alocal interconnect and respective select gates 304. A select gate 304scan be used to decouple the driver 300 from and couple the sensor 302to the desired line 28 when the respective cell 104 is read. When therespective cell 104 is written the opposite takes place; another selectgate 304 can decouple the line 28 from the sense circuit 302 and theline 28 is coupled to the driver 300. Of course, during this operation,another line 44 is also enabled by similar circuitry to address therespective cell. Alternatively, as a possible space-saving and/orfabrication simplifying arrangement, the driver circuit 300 and sensingcircuit 302 can be connected to the electrode line 28 at the sameterminal end.

The stacked memory cell and shared bit line/wordline array 100architecture allows for a higher density memory array 100 with fewermasks needed during fabrication. Also, this configuration provides alower cost in forming the array 100 and a simpler array layout. Theperiphery circuitry compensates for the simpler memory array layout tocontrol the common wordlines and bit lines, i.e., the layers ofelectrode lines 28, 44, and 58, and utilizes select gates to floatcircuitry not being used.

FIG. 19 shows how the memory array 100 can be connected with addressing,programming, and readout circuitry. Each level 200 of electrode lines12, 28, 44, 58, 72 is in electrical connection with a write accessdevice 202 and a sense access device 204, for example, an accesstransistor. The access devices 202, 204 electrically connect theelectrode lines 12, 28, 44, 58, 72, and thereby, the memory cells 102,104, 106, 108 (FIGS. 17 b and 17 d), which are between therepresentative electrode line levels 200, to row/column decode/enablecircuitry 206. The row/column decode/enable circuitry 206 connects totiming and control circuitry 208 and row driver circuitry 212, and toinput/output buffer/port circuitry 210 and sense and amplifier circuitry214. As indicated above, the connections to the addressing, programming,and readout circuitry can be provided at both terminal ends of thelines, e.g., 28, or at a single end of the lines, e.g., 28.

According to an embodiment of the invention, the array 100 undergoes abiasing scheme in which unselected, surrounding bit lines and unselectedwordlines the same level of an addressed memory cell are allowed tofloat, while simultaneously the selected, addressing bit line-wordlinepair is subjected to a current pulse so as to cause the diode structurein the target memory cell to be pulsed in a forward bias direction. Thedirection of the forward bias current in the target memory cell, e.g.,104, is consistent with the voltage difference V_(hi)-V_(lo), which willinduce the required programming current in the phase change material ofthe cell, e.g., 104. This current pulse may be induced by a conventionalvoltage pulse having a magnitude of 2.5 volts. This biasing schemecombined with the diode structure of the memory cells provides reducedleakage current in the array. With reduced leakage current, the array100 can be used in a wide range of applications, including as part of adedicated memory device used in applications in which power consumptionis a concern such as portable devices.

FIGS. 1 a to 17 e show stages of fabrication of a memory array 100 inaccordance with an embodiment. FIGS. 1 a and 1 b show a substrate 10upon which the array 100 can be fabricated. FIG. 1 a shows the substratefrom a top view and FIG. 1 b shows the substrate 10 through crosssection A-A. The substrate 10 can include logic circuits and all supportcircuitry (FIG. 19), formed on a semiconductor material under the areathat will support the memory array 100 (FIG. 17 b, for example).Preferably, the substrate is covered with an insulator layer 11, such asan oxide or silicon nitride layer, planarized to the tops of the supportcircuitry by chemical mechanical polishing if desired. These structuresare not shown, but can be formed according to standard processingtechniques known in the art.

As shown in FIGS. 2 a and 2 b, a layer of metal 12 can be deposited overthe substrate 10 and insulating material 11. The metal layer 12 cancomprise conductive materials such as titanium (Ti), tungsten (W),tungsten nitride (WN), titanium nitride (TiN), titanium tungsten (TiW),carbon (C), Silicon carbide (SiC), titanium aluminum nitride (TiAlN),titanium silicon nitride (TiSiN), polycrystalline silicon, tantalum(Ta), tantalum nitride (TaN), platinum (Pt), silver (Ag), gold (Au), andcombinations of such materials, for example a stack of TiN/WN/W with theTiN against the next-formed poly diode material 14, and can be depositedby known techniques, such as chemical vapor deposition, plasma enhancedchemical vapor deposition, evaporative techniques, and other methods.The metal layer 12 is preferably formed to be about 20 Å to about 2,000Å thick. A diode layer 14 can be formed over the metal layer 12. Thepoly diode material layer 14 can be made of p-type poly-Si, which withlater-formed silicide (e.g., CoSi₂ metal), forms Schottky barrier andbackside (ohmic) contact structures and can be formed by known methodsas well. A hard mask layer 16 is formed over the poly diode materiallayer 14. The hard mask 16 can be a nitride material and is preferablyformed to be about 20 Å to about 4,000 Å thick. As shown in FIGS. 2 aand 2 b, the metal layer 12, poly diode material layer 14, and hard masklayer 16 are formed as a blanket across the substrate 10 and insulatinglayer 11.

As shown in FIGS. 3 a and 3 b, the hard mask 16 is patterned with aphotoresist mask 18. As shown in FIGS. 4 a and 4 b, the hard mask 16,poly diode material layer 14, and metal layer 12 are etched using mask18 down to the substrate 10, or insulator 11 (which is shown in FIG. 4b), to leave stacked lines of these layers 12, 14, 16. As shown in FIGS.5 a and 5 b, sidewall spacers 20 are formed on the sides of the stackedlines of metal layer 12, diode layer 14, and hard mask 16. Thesesidewall spacers 20 are formed by deposition, for example, of a nitridematerial or silicon oxide (SiO_(x)) and can be deposited by atomic layerdeposition over the stacked lines 12, 14, and 16 and then etched toleave the sidewall spacers 20. A dielectric layer 22 is then formed overthe substrate 10 and insulating layer 11, covering the sidewall spacers20 and hard mask 16. The dielectric layer 22 is then planarized toexpose the hard mask 16. The dielectric layer 22 can be made of manyknown insulative materials, but is preferably silicon oxide(Si_(y)O_(x)).

As shown in FIGS. 6 a and 6 b, the hard mask 16 is removed selective tothe dielectric 22 and diode layer 14. The poly diode material layer 14is then selectively coated with a silicide diode material 24, such asCoSi₂, which is treated to enhance electron injection into a phasechange material to be formed thereover. This treatment can includeforming one or more nanoparticles on the silicide diode material 24,forming a band engineered crested barrier over the material 24, orroughening the surface of the material 24 to increase its ability toproduce high electric fields. Formation of the silicide material 24 overthe poly diode material 14 creates a Schottky diode structure.

As shown in FIGS. 7 a and 7 b, phase change material, such as Ge₂Sb₂Te₅(commonly referred to as GST), for example, is formed as a layer 26 overthe silicide diode material 24 and dielectric layer 22. Other knownphase change materials can be used for layer 26. The phase changematerial layer 26 can be deposited by sputtering, or other knowntechniques. An electrode layer 28 is formed over the phase changematerial layer 26 and can comprise metal or other conductive material.Preferably, the electrode layer 28 comprises the same material, e.g.,TiN/WN/W, as metal layer 12 and is formed to similar dimensions. Thiselectrode layer 28 completes the material layering for first plane 101(FIG. 17 b) of memory cells, including cell 102 (FIG. 17 b), and alsobegins the material layering for next overlying plane 103 (FIG. 17 b) ofmemory cells, including cell 104 (FIG. 17 d), of the memory array 100.

Another poly diode material layer 30 can be formed over the electrodelayer 28 and preferably comprises the same material, e.g., p-type poly,as diode layer 14. Another hard mask 32 is formed over the diode layer30. This hard mask 32 can comprise the same material, e.g., nitride, asthe first hard mask 16. As shown by FIGS. 8 a and 8 b, the hard mask 32is patterned with a photoresist mask 34. The photolithographic patternfor the photoresist mask 34 can be specifically designated and originalfor this plane 101 (FIG. 17 b) of cells, or the patterned mask used toform the photoresist mask 18 (FIG. 3 b) can be rotated 90 degrees andreused.

FIG. 8 b shows a cross section of the substrate 10 portion shown in FIG.8 a through line A-A, which runs through the photoresist mask 34. FIG. 8c shows a cross section of the substrate 10 portion of FIG. 8 a throughline B-B, which does not run through the photoresist mask 34. FIG. 8 dshows a cross section of the substrate portion 10 of FIG. 8 a throughline C-C, which is orthogonal to the cross sections through lines A-Aand B-B and through one of the stacked lines of layers 12, 14, and 24.FIG. 8 e shows a cross section of the substrate 10 portion shown in FIG.8 a through line D-D, also orthogonal to lines A-A and B-B, which runsthrough the dielectric layer 22. The cross section lines A-A, B-B, C-Cand D-D are respectfully maintained throughout the figures.

As shown in FIGS. 9 a, 9 d, and 9 e, using the respective single,patterned, photoresist mask 34, the hard mask 32, poly diode materiallayer 30, and electrode layer 28 are etched to the phase change materiallayer 26 to leave stacked lines of these layers 28, 30, 32, which can beorthogonal to the underlying lines of layers 12, 14 and 24. As shown inFIG. 9 b, layers 28, 30, and 32 are present through line A-A, but asshown in FIG. 9 c, they are not present through line B-B.

FIGS. 10 a, 10 d, and 10 e show that sidewall spacers 36 are formed onthe sides of the stacked layers 28, 30, and 32. As explained above withregard to sidewall spacers 20, sidewall spacers 36 can be formed bydepositing an insulating layer, e.g., silicon oxide or nitride material,over the stacked layers 28, 30, and 32 and etching. Next, as shown inFIGS. 11 a, 11 b, 11 c, 11 d, and 11 e, the sidewall spacer 36 etch iscontinued through the phase change material layer 26 and silicide layer24 to stop at the poly diode material 14 and singulate the silicidediode material layer 24 to prevent cross talk among memory cells, e.g.,102 (FIG. 17 b). Alternatively, this etch may be carried through thepoly diode material 14 and stop on layer 12, which singulates the entirediode structure. This etching of the sidewall spacers 36 does notrequire another mask and completes the definition of the memory cell102. A dielectric 38 is deposited to fill the trenches formed by thesidewall spacer 36 etch. The dielectric 38 can be planarized to the hardmask 32. Next, the hard mask 32 is removed selective to the dielectric38 and poly diode material layer 30. The poly diode material layer 30 isthen selectively coated with a silicide material 40, which is treated,e.g., by roughening, forming nanoparticles or crested barrier, etc., toenhance electron injection into a phase change material to be formedthereover. This silicide material layer 30, with the poly diode material30, forms a Schottky diode.

As shown in FIGS. 12 a, 12 b, 12 c, 12 d, and 12 e, a phase changematerial, such as GST, for example, is formed as a layer 42 over thesilicide 40 and dielectric layer 38. Other phase change materials canalso be used. The phase change material layer 42 can be deposited bysputtering, or other known techniques. An electrode layer 44 is formedover the phase change material layer 42 and can comprise metal or otherconductive material. Preferably, the electrode layer 44 comprises thesame material as metal layer 12 and electrode layer 28, e.g., a TiN/WN/Wstack, and is formed to similar dimensions. This electrode layer 44completes the material layering for a second plane 103 (FIG. 17 b) ofmemory cells, including cell 104 (FIG. 14 b), and begins as the firstmaterial layer for the overlying plane 105 (FIG. 17 b) of memory cells,including cell 106 (FIG. 17 b), of the memory array 100.

Another poly diode material layer 46 can be formed, for example, ofp-type poly, over the electrode layer 44 and preferably comprises thesame material as diode layers 14 and 30. Another hard mask 48 is formedover the poly diode layer 46. This hard mask 48 can comprise the samematerial, e.g., nitride, as the first hard mask 16 and second hard mask32. A patterned photoresist mask 49 is formed over the hard mask 48. Nomore than this single mask is needed in forming the respective plane 103(FIG. 17 b) of memory cells, e.g., 104 (FIG. 14 b). As with thepatterned mask 34, the pattern used to form mask 18 can be reused toform mask 49 if rotated back 90 degrees from the alignment use to formmask 34 or an original designated pattern can be used. Whether anoriginal and plan-specific or reused and rotated mask is used, no morethan a single mask per central memory cell plane, e.g., plane 103including memory cell 104, is required.

FIGS. 13 a, 13 b, and 13 c show that, as discussed above in relation tothe processing steps shown in FIGS. 9 a, 9 d, and 9 e, the hard mask 48is etched to the phase change layer 42 to leave stacks of layers 44, 46,and 48. FIGS. 14 a, 14 b, and 14 c show that sidewall spacers 54 areformed on the sides of the stacked layers 44, 46, and 48 (hard mask 48is shown in FIG. 13 b, for example). As explained above with regard tosidewall spacers 20 and 36, sidewall spacers 54 can be formed bydepositing an insulating layer over the stacked layers 44, 46, and 48and etching. The sidewall spacer 54 etch is continued through the phasechange material layer 42 and silicide diode material layer 40 tosingulate the silicide diode material layer 40 to prevent cross talkamong memory cells, e.g., 104 (FIG. 17 d). This etch step defines thestacked memory cell 104. Alternatively, this etch may be carried throughthe poly diode material 30 and stop on layer 28, which singulates theentire diode structure.

Next, as also shown in FIGS. 14 b, 14 c and 14 e, a dielectric 50 isdeposited to fill the trenches formed by the sidewall spacer 54 etch.The dielectric 50 can be planarized to the hard mask 48 (e.g., FIG. 13b). Next, the hard mask 48 is removed selective to the dielectric 46 andpoly diode material layer 50. The poly diode layer 46 is thenselectively coated with a silicide diode material 52, such as CoSi₂,which is treated, e.g., by roughening or adding nanoparticle(s) orforming a crested barrier, for enhancing electron injection into a phasechange material to be formed thereover. The silicide diode material 52forms a Schottky diode with the poly diode material 50.

As shown in FIGS. 15 a, 15 b, 15 c, 15 d, and 15 e, a phase changematerial, such as GST, for example, is formed as a layer 56 over thesilicide diode material 52 and dielectric layer 50. However, other phasechange materials can be used also. The phase change material layer 56can be deposited by sputtering, or other known techniques. An electrodelayer 58 is formed over the phase change material layer 56 and cancomprise metal or other conductive material. Preferably, the electrodelayer 58 comprises the same material, e.g., TiN/WN/W, as metal layer 12,electrode layer 28, and electrode layer 44 and is formed to similardimensions. This electrode layer 58 completes the material layers for athird plane 105 (FIG. 17 b) of memory cells, including cell 106 (FIG. 17d), and begins as the first material layer for the overlying plane 107(FIG. 17 b) of memory cells, including cell 108 (FIG. 17 b), of thememory array 100. Another poly diode layer 60 can be formed over theelectrode layer 58 and preferably comprises the same material, e.g.,p-type poly, as diode layers 14, 30, and 46. Another hard mask 62 isformed over the poly diode layer 60. This hard mask 62 can comprise thesame material, e.g., nitride, as the hard masks 16, 32, and 48.

FIGS. 16 a, 16 d, and 16 e show that, as discussed above in relation tothe processing steps shown in FIGS. 9 a and 13 a, the hard mask 62 ispatterned with photoresist (not shown) and etched to the phase changelayer 56 to leave stacks of layers 58, 60, and 62. Again, this is theonly patterned mask needed in forming this plane 105 (FIG. 17 b) ofmemory cells and can be an original pattern or the pattern used to formmask 34 can be reused. Whether an original or reused mask is used, nomore than a single mask per central memory cell plane, such as plane 105including memory cell 106, is required.

FIGS. 16 d and 16 e show that sidewall spacers 68 are formed on thesides of the stacked layers 58, 60, and 62 (hard mask 62 is shown inFIG. 15 d, for example). As explained above with regard to sidewallspacers 20, 36, and 54, sidewall spacers 68 can be formed by depositingan insulating layer, e.g., silicon oxide or nitride, over the stackedlayers 58, 60, and 62 and etching. The sidewall spacer 68 etch iscontinued through the phase change material layer 56 and silicide diodelayer 52 to stop at the poly diode layer 50 and singulate the silicidediodes layer 52 to prevent cross talk among memory cells, e.g., 106(FIG. 17 b). Alternatively, this etch may be carried through the polydiode material 46 and stop on layer 44, which singulates the entirediode structure. Next, as also shown in FIGS. 16 a, 16 c, 16 d, and 16e, a dielectric 64 is deposited to fill the trenches formed by thesidewall spacer 68 etch. The dielectric 64 can be planarized to the hardmask 62. Next, the hard mask 62 is removed selective to the dielectric64 and poly diode layer 60. The poly diode layer 60 is then selectivelycoated with a silicide diode material 66, which is treated for highelectron injection for phase change material to be formed thereover;this forms a Schottky diode.

As shown in FIGS. 17 a, 17 b, 17 c, 17 d, and 17 e, a phase changematerial, such as GST, for example, is formed as a layer 70 over thesilicide diode material 66 and dielectric layer 64. Again, other phasechange materials can be used. The phase change material layer 70 can bedeposited by sputtering, or other known techniques. An electrode layer72 is formed over the phase change material layer 70 and can comprisemetal or other conductive material. Preferably, the electrode layer 70comprises the same material, e.g., TiN/WN/W, as metal layer 12 andelectrode layers 28, 44, and 58 and is formed to similar dimensions.This electrode layer 58 completes the material layers for a fourth plane107 of memory cells, including cell 108, of the memory array 100.

Another hard mask 74 is formed over the electrode layer 72. Note, sincethis is the top electrode 72 stack in this embodiment, no diode need beincluded; however, this need not necessarily be the top electrode andadditional planes of memory cells could be included in the array 100 ifdesired. The hard mask 74 can comprise the same material, e.g., nitride,as the hard masks 16, 32, 48, and 62 and is preferably formed to thesame dimensions. FIGS. 17 a, 17 b, and 17 c show that, as discussedabove in relation to the processing steps shown in FIGS. 9 a, 13 a, and16 a, the hard mask 74 can be patterned with photoresist (not shown) andetched through the phase change layer 70 and silicide diode layer 66 toleave stacks of layers 66, 70, 72, and 74. Alternatively, this etch maybe carried through the poly diode material 60 and stop on layer 58,which singulates the entire diode structure. Note, no sidewall spacersare necessarily included in this top-most stack. Next, as also shown inFIGS. 17 a, 17 b, 17 c, and 17 e, a dielectric 76 is deposited to fillthe trenches formed defining the stacks of layers 68, 70, 72, and 74.The dielectric 76 can be planarized to the hard mask 74.

The method and structures described in relation to FIGS. 1 a through 17e, 19 and 20 provide a simpler and less expensive fabrication for athree-dimensional memory array. Because no more than a single patternedmask is required to fabricate memory cell planes 103 and 105, which arethe central planes of the embodiment shown, many processing stepsrequired of prior techniques, including the use of multiple, often many,patterned masks per layer of memory cells, can be omitted from thefabrication. Further, the use of shared interconnect lines, e.g., 44,further simplifies the array structure and also conserves valuable arraylandscape for other features, making for a denser memory device.

The above-described processing techniques for fabricating a memorydevice allow the use of a 248 nm (photolithographic) scanner, which mayinitially create 200 nm pitch line/space pairs with 34 nm alignmentcontrol. The array features can then be pitch multiplied to create masksof 50 nm pitch line/space pairs (nominally 25 nm each) on each array 100level. Because there is no tight alignment requirement in fabricatingthe array, one does not need the typical f/3 of 8 nm alignment budgetthat would require a state of the art photo tool (which could costbetween about $40-45 million) and may instead use a 248 nm photo tool(which typically cost between about $15-20 million) to create highdensity memory products. Thus manufacturing costs can be significantlyreduced by use of the above described processes, which allow forloosening the alignment requirement of the memory array.

FIG. 18 illustrates a simplified processor system 400, such as acomputer, including a memory circuit 448 employing an array of phasechange memory devices as shown in FIGS. 17 a-17 e fabricated inaccordance with the invention. A processor system, such as a computersystem, generally comprises a central processing unit (CPU) 444, such asa microprocessor, a digital signal processor, or other programmabledigital logic devices, which communicates with an input/output (I/O)device 446 over a bus 452. The memory circuit 448 communicates with theCPU 444 over bus 452, typically through a memory controller.

In the case of a computer system, the processor system may includeperipheral devices, such as a floppy disk drive 454 and a compact disc(CD) ROM drive 456, which also communicate with CPU 444 over the bus452. Memory circuit 448 is preferably constructed as an integratedcircuit. If desired, the memory circuit 448 may be combined with theprocessor, for example CPU 444, in a single integrated circuit.

The above description and drawings should only be consideredillustrative of exemplary embodiments that achieve the features andadvantages described herein. Modification and substitutions to specificprocess conditions and structures can be made. Accordingly, the claimedinvention is not to be considered as being limited by the foregoingdescription and drawings, but is only limited by the scope of theappended claims.

1. A method of forming a three-dimensional memory array, comprising:forming a first plane of variable resistance memory cells, a secondplane of variable resistance memory cells, and at least one centralplane of variable resistance memory cells between said first and secondplanes; and using no more than one patterned mask per each central planeto form the respective variable resistance memory cells.
 2. The methodof claim 1, further comprising forming variable resistance memory cellsof adjacent planes such that they share memory cell interconnect lines.3. The method of claim 1, further comprising forming the variableresistance memory cells of the planes to each comprise a variableresistance material in electrical communication with an associateddiode.
 4. The method of claim 1, wherein the variable resistance memorycells are phase change memory cells.
 5. The method of claim 4, whereinsaid phase change memory cells comprise Ge₂Sb₂Te₅.
 6. The method ofclaim 1, further comprising forming the memory cells of each plane ofthe at least one central plane using a single patterned mask etchingstep and a sidewall spacer etching step, respectfully.
 7. The method ofclaim 6, comprising forming at least two central planes of variableresistance memory cells.
 8. The method of claim 7, further comprisingforming the memory cells of both of the at least two central planesusing a single mask.
 9. The method of claim 8, wherein said single maskis rotated with respect to the array between forming the memory cells ofa first central plane and forming the memory cells of a second centralplane.
 10. The method of claim 1, wherein forming the memory cells ofthe at least one central plane comprises: forming a first electrodeline; forming a diode over the first electrode line; forming a phasechange material over the diode; and forming a second electrode line overthe phase change material.
 11. The method of claim 10, wherein saidfirst and second electrode lines are orthogonal to one another.
 12. Themethod of claim 10, wherein the first and second electrode linescomprise stacks of TiN/WN/W.
 13. The method of claim 10, wherein thediode comprises p-type poly and CoSi₂.
 14. The method of claim 13,further comprising treating the CoSi₂ to enhance electron injection intothe phase change material.
 15. The method of claim 10, furthercomprising forming insulating sidewalls on the first electrode line anddiode.
 16. The method of claim 10, further comprising forming at least asecond central plane of variable resistance memory cells, comprising:forming a second diode over the second electrode line; forminginsulating sidewalls on the second electrode line and second diode;forming a second phase change material over the second diode; andforming a third electrode line over the second phase change material.17. The method of claim 1, wherein the respective memory cells in saidplanes are arranged in a cross point architecture.
 18. A method offorming a memory device, comprising: forming a first electrode line overa substrate; forming a first diode over the first electrode line;forming a first phase change material over the first diode; forming asecond electrode material over the first phase change material; forminga second diode over the second electrode material; forming a firstpatterned mask over the second diode; using the first patterned mask,etching the second diode, and the second electrode, stopping at thefirst phase change material, so as to form a second electrode line ofthe second electrode material in a crossing arrangement with the firstelectrode line; forming a first dielectric material over the seconddiode, the second electrode line, and the first phase change material;and etching the first dielectric material to leave sidewall spacers onthe second diode and second electrode material and continuing the etchthrough the first phase change material.
 19. The method of claim 18,further comprising: forming a second phase change material over thesecond diode; forming a third electrode material over the second phasechange material; forming a third diode over the third electrodematerial; forming a second patterned mask over the third diode; usingthe second patterned mask, etching the third diode, and the thirdelectrode material, stopping at the second phase change material, so asto form a third electrode line of the third electrode material in acrossing arrangement with the second electrode line; forming a seconddielectric material over the third diode, the third electrode line, andthe second phase change material; and etching the second dielectricmaterial to leave sidewall spacers on the third diode and thirdelectrode line and continuing the etch through the second phase changematerial.
 20. The method of claim 19, further comprising: forming afirst silicide material as part of the first diode; forming a secondsilicide material as part of the second diode; and forming a thirdsilicide material as part of the third diode.
 21. The method of claim20, further comprising: forming a third phase change material over thethird silicide material; forming a fourth electrode material over thethird phase change material; forming a fourth diode over the fourthelectrode material; forming a third patterned mask over the fourthdiode; using the third patterned mask, etching the fourth diode, and thefourth electrode material, stopping at the third phase change material,so as to form a fourth electrode line from the fourth electrode materialin a crossing arrangement with the third electrode line; forming a thirddielectric material over the fourth diode, the fourth electrode line,and the third phase change material; etching the third dielectricmaterial to leave sidewall spacers on the fourth diode and fourthelectrode line and continuing the etch through the third phase changematerial; forming a fourth silicide as part of the fourth diode; forminga fourth phase change material over the fourth silicide; forming a fifthelectrode material over the fourth phase change material; forming a hardmask material over the fifth electrode material; forming a fourthpatterned mask over the hard mask material; using the fourth patternedmask, etching the hard mask material, the fifth electrode material, thefourth phase change material, and the fourth silicide, stopping at thefourth diode so as to form a fifth electrode line from the fifthelectrode material in a crossing arrangement with the fourth electrodeline; forming a fourth dielectric material over the hard mask material,the fifth electrode line, the fourth phase change material, the fourthsilicide, and the fourth electrode line.
 22. The method of claim 18,wherein said phase change material comprises Ge₂Sb₂Te₅.
 23. The methodof claim 18, wherein after forming the first electrode line, the firstpatterned mask is the only mask used to define a first plane of memorycells.
 24. The method of claim 19, wherein after forming the firstelectrode line, the first patterned mask and the second patterned maskare the only masks used to define a first plane of memory cells and asecond plane of memory cells, respectively.
 25. The method of claim 21,wherein after forming the first electrode line, the first patternedmask, the second patterned mask, the third patterned mask, and thefourth patterned mask are the only masks used to define a first plane ofmemory cells, a second plane of memory cells, a third plane of memorycells, and a fourth plane of memory cells, respectively.
 26. A memorydevice comprising: a first plane comprising a first phase change memorycell, which comprises a first electrode line and a second electrodeline, with a first phase change memory element and a first diodeconnected in series between said first and second electrode lines; asecond plane in a stacked configuration with said first plane andcomprising a second phase change memory cell, which comprises the secondelectrode line and a third electrode line, with a second phase changememory element and second diode connected in series between the secondand third electrode lines; and a third plane in a stacked configurationwith said first and second planes and comprising a third phase changememory cell, which comprises the third electrode line and a fourthelectrode line, with a third phase change memory element and third diodeconnected in series between the third electrode line and fourthelectrode line.
 27. The memory device of claim 26, wherein the first andsecond electrode lines are respectively configured in a cross pointarchitecture, the second and third electrode lines are respectivelyconfigured in a cross point architecture, and the third and fourthelectrode lines are respectively configured in a cross pointarchitecture.
 28. The memory device of claim 26, wherein the first,second and third phase change memory cells are in respective stackedplanes so as to form a three-dimensional array of memory cells.
 29. Thememory device of claim 28, wherein each of said first, second and thirdmemory cells is addressed by X, Y, and Z memory addresses.
 30. Thememory device of claim 26, wherein each of the first, second and thirdmemory cells comprises a respective silicide layer as a part of itsrespective diode.
 31. The memory device of claim 26, wherein said memorydevice is part of a processor system.
 32. The memory device of claim 26,wherein at least the second and third electrode lines are selectivelyconnectable to both a driver circuit and a sense circuit.
 33. The memorydevice of claim 32, wherein only one of the driver circuit and sensecircuit is in direct electrical communication with a respectiveelectrode line at any time.
 34. A memory cell, comprising: a phasechange element in series with a diode; a first electrode lineelectrically connected to the diode opposite the phase change element; asecond electrode line electrically connected to the phase change elementopposite the diode; where each of the first electrode line and secondelectrode line is respectively electrically connected to a drivercircuit and a sense circuit and at least one of the first electrode lineand second electrode line is shared with another memory cell.
 35. Thememory cell of claim 34, wherein the first electrode line and the secondelectrode line are arranged in a cross point architecture.
 36. Thememory cell of claim 34, wherein the first electrode line and the secondelectrode line are electrically respectively connected to the drivercircuit and the sense circuit by respective access devices.
 37. Thememory cell of claim 34, wherein the respective driver circuit and sensecircuit are connected to the first and second electrode lines atdifferent terminal ends of the first and second electrode lines.
 38. Thememory cell of claim 34, wherein the respective driver circuit and sensecircuit are connected to the first and second electrode lines at thesame terminal ends of the first and second electrode lines,respectively.
 39. The memory cell of claim 34, wherein the memory cellis par of a three dimensional memory array wherein the memory cell isaddress by an X, a Y, and a Z address coordinate.
 40. A memory device,comprising: an array of memory cells arranged in a plurality of stackedplanes of said memory cells, wherein each of said memory cells comprisesa memory element at the intersection of a respective top electrode lineand a respective bottom electrode line, the respective top and bottomelectrode lines having a line width, said memory element having aminimum feature dimension of f; wherein at least two of said planes ofmemory cells share respective shared electrode lines, said sharedelectrodes lines being the top electrode lines of an underlying planeand the bottom electrodes lines of an overlying plane; and wherein thewidth of the respective top electrode lines define the f dimension forrespective underlying memory cell elements.
 41. The memory device ofclaim 40, wherein said memory elements have a 4 f footprint per memoryelement.
 42. The memory device of claim 40, further comprising at leastfour said planes of memory cells.
 43. The memory device of claim 42,wherein said memory elements have a 1 f footprint per memory.
 44. Thememory device of claim 40, further comprising an access device betweeneach respective bottom electrode and the associated respective memoryelement.
 45. The memory device of claim 44, wherein the access device isa two-terminal device.
 46. The memory device of claim 44, wherein theaccess device is a diode.
 47. The memory device of claim 44, wherein theaccess device is a threshold switching device.
 48. The memory device ofclaim 40, wherein the f dimension is between about 18 nm to about 50 nm.49. The memory device of claim 40, wherein the memory element comprisesa phases change material.
 50. The memory device of claim 49, wherein thephase change material comprises Ge₂Sb₂Te₅.
 51. The memory device ofclaim 40, wherein the respective top electrode lines are arranged in aline/space pattern.
 52. The memory device of claim 40, wherein therespective top and bottom electrodes are not parallel to each other. 53.The memory device of claim 40, wherein the respective top and bottomelectrodes lines are orthogonal to each other.